Spring @RequestParam

🔍 What Is It?

@RequestParam binds HTTP request parameters to method arguments.

Sources it reads from:

• →Query string: GET /products?category=electronics
• →Form data: POST with application/x-www-form-urlencoded
• →Multipart form: POST with multipart/form-data

Key attributes:

• →name / value — parameter name; specify it explicitly to avoid relying on compiler parameter-name metadata
• →required — default true; false makes it optional
• →defaultValue — used when the parameter is absent or empty; also makes it optional

Required, optional, and default values

These examples assume Spring MVC's standard binding configuration. A custom converter can change how empty text is handled. An invalid integer such as ?page=abc fails conversion; defaultValue does not replace malformed values. For an optional numeric parameter without a default, use Integer or Optional<Integer> rather than a primitive int.

Supported types:

• →Primitives: int, long, boolean
• →Wrappers: Integer, Long, Boolean
• →String, Date, LocalDate
• →Enums (by name)
• →List<String> for multi-value params
• →MultiValueMap<String, String> for all params

🎯 Why Do We Need It?

Query parameters are the standard way to pass filtering, sorting, pagination, search text, and optional flags in Spring Boot REST APIs. @RequestParam gives you type-safe binding, automatic conversion, validation, and default values, which is much cleaner and safer than manually reading HttpServletRequest.getParameter().

🏗️ What Happens in Real Projects?

Used in every list/search endpoint:

• →GET /products?category=electronics&minPrice=100&maxPrice=500&page=0&size=20&sort=price,asc
• →GET /orders?status=PENDING&customerId=123&from=2024-01-01&to=2024-12-31
• →GET /users?search=john&role=ADMIN&active=true

⚙️ How It Works

Spring's argument resolvers read request parameters and convert them to the declared Java type through ConversionService. That means "42" becomes int 42, "true" becomes boolean true, "2026-08-27" can become LocalDate, and enum strings like "ACTIVE" can bind to Status.ACTIVE when the type is declared correctly.

💻 Example

Request Parameters in Practice — Filtering, pagination, and optional parameters.

import java.util.List;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class RequestParamDemoController {
    @GetMapping("/hello")
    public String hello(
            @RequestParam(name = "name", defaultValue = "World") String name) {
        return "Hello, " + name;
    }

    @GetMapping("/tags")
    public List<String> tags(@RequestParam(name = "tag") List<String> tags) {
        return tags;
    }
}

// GET /hello                  -> Hello, World
// GET /hello?name=Sam          -> Hello, Sam
// GET /hello?name=             -> Hello, World
// GET /tags?tag=spring&tag=java -> ["spring", "java"]

🤔 Common Confusions

🚨 Common Production Issues

✅ Best Practices

🏛️ Architect's Note

💬 Frequently Asked Questions

🎯 Key Takeaways

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